1. Field of the Invention
The present invention relates to an antenna probe, a low noise converter with an antenna probe, and a method of connecting an antenna probe.
2. Description of the Background Art
For receiving signals of satellite broadcast or satellite communication, a reception system including an antenna apparatus has been used.
FIG. 11 schematically shows a general satellite broadcast receiving system. An incoming signal from a broadcasting satellite 33 represented by an arrow 74 is reflected at a surface of an reflected board 35, and received by a low noise (LNB: Low Noise Block down) converter 32. Low noise converter 32 performs frequency-conversion on weak radio wave of 12 GHz band coming from broadcasting satellite 33 to a signal of an IF (Intermediate Frequency) band of 1 GHz.
Low noise converter 32 amplifies the signal in a low-noise state, and transmits the signal through an IF cable 34 to a DBS (Direct Broadcasting Satellite) tuner 31. The signal from the satellite comes in a frequency, for example, of 12.20 to 12.75 GHz. The signal has its frequency converted by low noise converter 32, and is transmitted to DBS tuner 31 with the frequency of 1000 to 1550 MHz. DBS tuner 31 processes the received signal in an internal circuit, and transmits the resulting signal to a television receiver 30. Television receiver 30 displays an image or a video image based on the received signal.
The area 61 represented by the dotted line is an indoor area and apparatuses herein are arranged indoors. Television receiver 30 and DBS tuner 31 are arranged indoors.
FIG. 12 shows an exemplary block diagram of an electric circuit formed in the low noise converter. The incoming signal having the frequency in 12 GHz band is led to a waveguide in low noise converter 32. Inside the waveguide, antenna probes 52 and 53 are arranged, and the incoming signal is received by antenna probes 52 and 53.
The signal received by antenna probes 52 and 53 is transmitted to an LNA (Low Noise Amplifier) 40. LNA 40 amplifies the signal. LNA 40 includes an amplifier 41 for amplifying an output signal from antenna probe 53, an amplifier 42 for amplifying an output signal from antenna probe 52, and an amplifier 43 for amplifying these output signals.
The signal amplified by LNA 40 is transmitted to a mixer 46 through a filter 45. As filter 45, a BPF (Band Pass Filter) is used, which passes a desired frequency band and filters out a signal in the image frequency band. In mixer 46, an output signal of a local oscillator 48 is synthesized and the signal is converted to have an intermediate frequency. The output signal from mixer 46 is amplified by an intermediate frequency amplifier 47, and transmitted to an output terminal 50 with appropriate noise and gain characteristics. Electric power is supplied by a power source 49 to these components.
Low noise converter 32 includes a waveguide and an antenna probe for receiving the incoming signal.
FIG. 13 is a schematic perspective view of the waveguide having the antenna probe arranged inside. FIG. 14 is a cross section taken along the line XIV-XIV of FIG. 13. The radio wave reflected at the reflected board enters the waveguide in a direction represented by an arrow 71. The incoming signal represented by the arrow 71 includes orthogonally crossing, two polarized waves. The incoming signal includes a plane of polarization parallel to the direction represented by the arrow 75 and a plane of polarization parallel to the direction represented by the arrow 76. The planes of polarization are orthogonal to each other. For example, the signal parallel to the direction of the arrow 75 represents a plane of vertical polarization, while the signal parallel to the direction of the arrow 76 represents a plane of horizontal polarization.
In waveguide 51, antenna probes 52 and 53 for receiving the polarized signals having respective planes of polarization are arranged. Antenna probe 52 receives a signal having the plane of polarization parallel to the direction of the arrow 75, while antenna probe 53 receives a signal having the plane of polarization parallel to the direction of the arrow 76.
Referring to FIG. 14, antenna probes 52 and 53 are arranged such that directions of extension cross orthogonally with each other. Referring to FIG. 13, antenna probes 52 and 53 are arranged apart from each other in a direction of extension of waveguide 51.
Waveguides including such antenna probes are disclosed, for example, in Japanese Patent Laying-Open Nos. 10-261902 and 2000-261202. The antenna probes are formed as bars and fixed on the waveguides.
FIG. 15 is a schematic perspective view of one antenna probe in accordance with the prior art, and FIG. 16 is a schematic perspective view of another antenna probe in accordance with the prior art.
Referring to FIG. 15, an antenna probe 54 includes an antenna portion 56 formed of metal in a circular column and a connecting portion 57 for connection to a circuit board. Connecting portion 57 is formed by processing a tip end of antenna portion 56 as a metal bar. Connecting portion 57 is joined to a micro-strip line formed on the circuit board by soldering.
Referring to FIG. 16, an antenna probe 55 includes an antenna portion 56 formed of a conductor in a circular column, a fixing portion 59 for fixing antenna probe 55 to a box or the like in which the waveguide is formed, and a connecting portion 58 for connection to a circuit board. Fixing portion 59 is formed, for example, of resin, and arranged to surround a portion of antenna portion 56.
FIG. 17 is a schematic perspective view of the antenna probe of FIG. 15 arranged on a waveguide. FIG. 18 is a cross section taken along the line XVIII-XVIII of FIG. 17. FIG. 19 is a plan view of the circuit board in accordance with the prior art.
On a surface of circuit board 6, a micro-strip line 9 is formed, and through micro-strip line 9 and circuit board 6, antenna probe 54 is arranged. Antenna probe 54 is arranged such that a part of antenna portion 56 is positioned inside the waveguide 51. Connecting portion 57 formed at one end of antenna probe 54 is fixed on micro-strip line 9 by soldering.
As can be seen from FIGS. 15 to 18, according to the prior art, a bar-shaped antenna probe is fixed on a box of the waveguide or on a circuit board.
Referring to FIGS. 17 and 18, according to the method of fixing connecting portion 57 of antenna probe 54 to circuit board 6, antenna probe may possibly be inclined in the direction represented by an arrow 72 or 73 when antenna probe 54 is fixed, and hence, assembly has been difficult. Further, if antenna probe 54 should be inclined, it is necessary to adjust the angle of attachment using a jig or the like for correcting inclination, which is very troublesome.
Further, when antenna probe 54 is attached, it is difficult to visually observe antenna portion 56 from the surface side of the circuit board, and hence it is difficult to inspect inclination of antenna probe 54.